Review on Soil Solidification and Heavy Metal Stabilization by Microbial-Induced Carbonate Precipitation (MICP) Technology

Microbial-induced carbonate precipitation (MICP) as a novel eco-friendly bioremediation method has been applied tentatively in soil solidification and heavy metal stabilization. In order to deeply study the theoretical knowledge of MICP and its application in environmental engineering, this review summarizes the main mechanisms of MICP, including biosorption and biomineralization. It is proposed innovatively that bacterial cell wall and extracellular polymeric substances (EPS) can provide ions binding sites during the process of biomineral nucleation due to negative charges and functional groups. Engineering properties of soil are regulated, such as increase of unconfined compressive strength (UCS) and shear stress, decrease of permeability and improvement of erosion resistance. Supposing the available CaCO3 content (CCC), UCS can be estimated by two boundary lines with an intersection angle of 2.72°. The great bioremediation capacity of metal cations/anions greatly depends upon carbonate precipitation/coprecipitation. Biotransformation and bioaccumulation of metal poisonousness should be considered as essential mechanisms in bacteria. Finally, according to the authors' knowledge, current deficiencies and future research directions for the technology were pointed out, which might be beneficial to the optimization, application and generalization of MICP technology.